Over 30% of adolescents are currently overweight and 20% are obese. Given the chronic health concerns and premature mortality associated with excess body weight, identification of early, modifiable risk factors is crucial to obesity prevention. Some data suggest that increases in energy intake may account for the high rates of pediatric obesity. Clarification of specific mechanisms that promote increases in energy intake may inform the development of novel interventions that focus on these underlying processes. The cognitive capacity theory suggests that [adolescents] who exert sustained periods of mental effort may be more susceptible to increased energy intake due to simultaneous increases in behavioral disinhibition and reliance on immediate rewards. Although brief cognitive tasks induce increased energy intake in adults, the cognitive capacity model for energy intake has not been tested in youth. Thus, the purpose of the current proposal is to evaluate a novel cognitive capacity model for regulating energy intake that proposes that cognitive fatigue induces excess weight gain in youth. The model specifies factors that have been linked to disinhibited eating and excess weight in youth, and are likely to exacerbate the proposed relationship between cognitive fatigue and energy intake, including food reinforcement, poor sleep and executive dysfunction. The first aim for the current proposal includes validating a cognitive fatigue paradigm in [40 adolescents] by examining changes in state fatigue and task resistance, as well as task performance over the course of a 2-hour vigilance task. The second aim involves a 2-condition cross-over design in which 110 boys and girls (1[3]-17 yo; 50% non-overweight, 50% obese) will be assigned in random order to two conditions: 1) cognitive fatigue; and 2) control (non-fatiguing). Following both conditions, energy intake will be assessed during a large multi-array buffet test meal. Food reinforcement, sleep behavior, and executive functioning will be assessed via behavioral laboratory tasks, wrist actigraphy, and neuropsychological tests, respectively. Participants will also attend a 1-year follow-up visit, during which weight and adiposity will be reevaluated. It is hypothesized that energy intake will be greater in the cognitie fatigue than in the control condition and fatigue-associated intake will predict increases in weigh and adiposity one year later. Proposed moderators of the link between cognitive fatigue and energy intake include higher food reinforcement, poorer sleep quality, and lower executive functioning performance. Findings from the current application may identify important processes to target in obesity interventions. Results will also provide clinically significant information regarding individual and situational factors associated with increased energy intake and excess weight gain in [adolescents], thereby elucidating some of the phenotypic variability in pediatric obesity. The training plan will also provide unique multidisciplinary training in conceptual and technical research skills needed to carry out this multi-modal study, including advanced training and mentorship in the objective evaluation of sleep and eating behavior, as well as longitudinal analyses.